Sitting is the most frequent body posture: we sit at work, at school, in the car, on the bus, on the train, in an airplane, and so on. Those who are wheelchair-bound are in seated positions for an entire day.
A seat should take the weight off one's feet in order to lessen stress on the legs, and the seat should provide some postural stability while one works or relaxes. One should also be able to relax muscles that are at rest.
Seat height should not be so high that the occupant's legs are left dangling. This would mean that there would be pressure on the soft tissues under the thighs. This pressure can interfere with the return of blood from the lower limbs, which may cause tingling and numbness in the thighs due to pressure on blood vessels and nerves.
At the same time, there exists an opinion that prolonged travel in a seated position can cause venous stasis, which means loss of proper function of the veins that carry blood back to the heart from a person's legs.
N. S. Lee, et al, showed in their “Review of Selected Literature Related to Seating Discomfort” submitted in 1990 to Ikeda Engineering Corporation, Mich., USA, that in terms of ml/min/100 ml of body segment, blood flow in the leg of a person (4 ml/min/100 ml) in a seated position is much lower than, e.g., in the arm (10 ml/min/100 ml). This means that the legs of a seated person are to a greater extent subject to tingling and numbness in the thighs caused by pressure on blood vessels and nerves.
It is understood that in the body of a person seated on a chair or on a similar support, the aforementioned abnormalities of blood circulation are caused by areas on the chair that cause increased pressure on the thighs. In the majority of cases, such areas are the edges of a seat.
Attempts have been made to improve a seat support for redistribution of pressure on the buttocks. For example, Pain Reliever Co., KS, distributes a G-Seat Gel Cushion (hereinafter referred to as “G-Seat Gel Cushion”) for improved blood circulation. (See Http://www.autosportcatalog.com/index.cfm/fa/p/pid/2168/cid/57/sc/2737)
The G-Seat Gel Cushion uses viscoelastic gel and a functional design to disperse pressure and to improve the level of comfort wherever one is seated. The G-Seat Gel Cushion features a center relief groove that eliminates soft-tissue compression and suspends the tailbone (coccyx), therefore eliminating direct pressure on the spine.
Pressure redistribution occurs because the gel that fills the seat works like a liquid and conforms to the body part, i.e., the buttocks. In other words, pressure on the buttocks and thigh surfaces in contact with the G-seat Gel Cushion is redistributed in accordance with Pascal's Law, i.e., in a normal direction and essentially uniformly at all points of contact. However, since the G-seat Gel Cushion is substantially flat, the problem is solved only partially. In other words, localized areas of increased pressure will still exist on the boundaries of the G-seat Gel Cushion.
German Patent Publication DE10200500243 published on Jul. 27, 2006 (inventor A. Wunder, et al) discloses a chair with a seat that has a backrest, cushion, and adjustable thigh support. The thigh support comprises a U-shaped unit that is arranged across the chair under the thighs of the occupant and is adjustable opposite the cushion. A gap is formed between the cushion and the U-shaped unit during adjustment of the U-shaped unit opposite to the cushion. The gap is coverable by an adjustment device, and the cushion is composed of a foam material. The above-described thigh support does not solve the aforementioned problem of localized pressure on the thigh surfaces at the edge of the transverse thigh support and, instead, only shifts the position of the edge.
A number of patents, such as U.S. Pat. No. 4,636,002 (published on Jan. 13, 1987, inventor T. Genjiro), U.S. Pat. No. 4,712,834 (published on Dec. 15, 1987, inventor J. Warrick, et al), and U.S. Pat. No. 4,838,509 (published on Jun. 13, 1989, inventor J. Klink, et al), etc., disclose car seats with adjustable features that include thigh supports. However, all of these devices are permanently built into the structure of the seat, operate with the use of complicated and expensive mechanisms, and change only vertical and angular positions of the transverse thigh support.
U.S. Pat. No. 5,083,551 issued in 1992 to K. Addison, Jr. discloses a method and apparatus for providing improved blood circulation to a person seated in a wheelchair or stationary chair used by handicapped persons, or by those who must remain inactive in a seated position for extended periods of time. The apparatus imparts an undulating, wave-like motion to the flexible seat portion of the chair which stimulates circulation of blood in the lower extremities and prevents development of ischemic or decubitus ulcers by providing changing points of pressure on the buttocks and thighs of a seated individual. The apparatus is connected to a wheelchair or chair and is powered by a storage battery mounted thereon.
U.S. Pat. No. 7,093,898 issued in 2006 to L. De Guevara discloses a portable air-pressure-applying assembly for seats. Proposed in this patent is an air-pressure-applying assembly for a seat, having an occupant-holding portion for selectively applying the desired pressure to the body of the seated occupant. This assembly includes an air-bag assembly, an air-pressure source, an inlet-conduit assembly, an exhaust valve assembly, and a control assembly. The air-bag assembly is removably attached to the seat occupant-holding portion. The inlet-conduit assembly is in fluid communication at one end with the air-pressure source and at another source with the air-bag assembly. The exhaust valve assembly is in fluid communication at one end with the inlet conduit assembly and has an air outlet at the other end. A control assembly is linked to the air pressure source and to the exhaust valve assembly. The control assembly is configured so as to selectively signal the air-pressure source to inflate the air bag assembly in order to apply the desired pressure to the body of the seat occupant and to selectively signal the exhaust valve assembly to release air from the air-bag assembly.
In order to solve the above problem, the inventor herein has developed a pad for supporting the thigh of a person seated on a seat in a position that alleviates pressure applied to the lower surface of the thigh and thus for improving blood circulation through the leg without numbness or similar phenomena associated with long-time sitting. This pad is disclosed in U.S. Pat. No. 7,255,396 issued to the applicant of the present patent application in 2007. The pad is made in the form of a soft deformable body filled, e.g., with silicone gel. The pad has a flat rectangular bottom surface and curvilinear lateral sides. In the plane perpendicular to the bottom, the pad has a triangular cross-section with heights of the triangles gradually reduced from one end face of the pad to the opposite end face of the pad so that the ridge that connects the apexes of the triangular cross-sections from one end face to the other is inclined with respect to the flat bottom.
In further development of the above idea, the applicant of the present patent application invented a self-inflatable thigh support, which is disclosed in pending U.S. patent application Ser. No. 12/011,316 filed on Jan. 26, 2008. The thigh support is made in the form of an elongated body of a triangular cross-section that consists of an airproof inner casing made from a nonstretchable flexible material and a squeezable foam plastic that fills the interior of the casing. The casing is provided with a valve that can be opened for squeezing the pad to the compressed state and then closed for preserving the pad in the compressed state, which is convenient for storage and transportation. To use the pad, the valve is opened, the squeezed foam plastic is expanded, and then the valve is closed, whereby the pad is maintained in a predetermined shape and with a predetermined rigidity. An advantage of this thigh support is that it can be deflated and squeezed to small dimensions that are convenient for storage and transportation. Another advantage is that rigidity of the support in the inflated state can be adjusted by releasing a portion of air trapped in the fully inflated thigh support.
It has been stated in the aforementioned pending patent application that the use of a thigh support of the aforementioned type alleviates pressure applied to the lower surface of the thigh and thus improves blood circulation through the leg without numbness or similar phenomena associated with long-time sitting. However, this statement is qualitative because no one has tried to measure the degree to which use of such support can improve blood circulation in the legs of a seated person nor the geometry, rigidity, or elasticity required of such thigh support for the most optimal blood circulation.